[QUIZ] Chess960 (#106)

ruby-talk
1

My solution:

=begin

import Data.List
import Data.Maybe

pieces = "RNBKQBNR"

permutation = []
permutation xs = [x:y | x <- nub xs, y <- permutation $ delete x xs]

restriction position =
  r1 < k && k < r2 &&
  sum (elemIndices 'B' position) `mod` 2 /= 0
  where
  r1:r2:_ = elemIndices 'R' position
  k = fromJust $ elemIndex 'K' position

results = filter restriction (permutation pieces)

=end

def permutation(pieces)
  return [pieces] if pieces.length <= 1
  result =
  pieces.uniq.each do |p|
    _pieces = pieces.dup
    _pieces.delete_at(pieces.index(p))
    permutation(_pieces).each do |perm|
      result << (perm << p)
    end
  end
  result
end

results = permutation("RNBKQBNR".split(//)).select do |position|
  r1 = position.index('R')
  r2 = position.rindex('R')
  b1 = position.index('B')
  b2 = position.rindex('B')
  k = position.index('K')
  r1 < k && k < r2 && ((b1+b2) % 2 != 0)
end

puts "Total positions = #{results.length}"
puts results[rand(results.length)].join(' ')

2

Very nice, compact solution. But what programing language is that in the block comment? I don't recognize it.

Regards, Morton

···

On Dec 19, 2006, at 11:43 PM, David Tran wrote:

My solution:

=begin

import Data.List
import Data.Maybe

pieces = "RNBKQBNR"

permutation = []
permutation xs = [x:y | x <- nub xs, y <- permutation $ delete x xs]

restriction position =
  r1 < k && k < r2 &&
  sum (elemIndices 'B' position) `mod` 2 /= 0
  where
  r1:r2:_ = elemIndices 'R' position
  k = fromJust $ elemIndex 'K' position

results = filter restriction (permutation pieces)

=end

def permutation(pieces)
return [pieces] if pieces.length <= 1
result =
pieces.uniq.each do |p|
   _pieces = pieces.dup
   _pieces.delete_at(pieces.index(p))
   permutation(_pieces).each do |perm|
     result << (perm << p)
   end
end
result
end

results = permutation("RNBKQBNR".split(//)).select do |position|
r1 = position.index('R')
r2 = position.rindex('R')
b1 = position.index('B')
b2 = position.rindex('B')
k = position.index('K')
r1 < k && k < r2 && ((b1+b2) % 2 != 0)
end

puts "Total positions = #{results.length}"
puts results[rand(results.length)].join(' ')